Method of making polycrystalline diamond with working surfaces depleted of catalyzing material

ABSTRACT

Griffin, Nigel, et al78.1081-1.3-29 Disclosed is a method for manufacturing a polycrystalline diamond or diamond-like element with greatly improved wear resistance without loss of impact strength. These elements are formed with a binder-catalyzing material in a high-temperature, high-pressure (HTHP) process. The PCD element has a body with a plurality of bonded diamond or diamond-like crystals forming a continuous diamond matrix that has a diamond volume density greater than 85%. Interstices among the diamond crystals form a continuous interstitial matrix containing a catalyzing material. The diamond matrix table is formed and integrally bonded with a metallic substrate containing the catalyzing material during the HTHP process. The diamond matrix body has a working surface, where a portion of the interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material. Typically, less than about 70% of the body of the diamond matrix table is free of the catalyzing material.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Divisional of U.S. patent application Ser.No. 09/682,419 filed on Aug. 30, 2001 which claims priority from U.S.Provisional Patent Application No. 60/234,075 filed Sep. 20, 2000, andfrom U.S. Provisional Patent Application No. 60/281,054 filed Apr. 2,2001.

BACKGROUND OF INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to superhard polycrystalline materialelements for wear, cutting, drawing, and other applications whereengineered superhard surfaces are needed. The invention particularlyrelates to polycrystalline diamond and polycrystalline diamond-like(collectively called PCD) elements with greatly improved wear resistanceand methods of manufacturing them.

[0004] 2. Description of Related Art

[0005] Polycrystalline diamond and polycrystalline diamond-like elementsare known, for the purposes of this specification, as PCD elements. PCDelements are formed from carbon based materials with exceptionally shortinter-atomic distances between neighboring atoms. One type ofdiamond-like material similar to PCD is known as carbonitride (CN)described in U.S. Pat. No. 5,776,615. In general, PCD elements areformed from a mix of materials processed under high-temperature andhigh-pressure into a polycrystalline matrix of inter-bonded superhardcarbon based crystals. A common trait of PCD elements is the use ofcatalyzing materials during their formation, the residue from which,often imposes a limit upon the maximum useful operating temperature ofthe element while in service.

[0006] A well known, manufactured form of PCD element is a two-layer ormulti-layer PCD element where a facing table of polycrystalline diamondis integrally bonded to a substrate of less hard material, such astungsten carbide. The PCD element may be in the form of a circular orpart-circular tablet, or may be formed into other shapes, suitable forapplications such as hollow dies, heat sinks, friction bearings, valvesurfaces, indentors, tool mandrels, etc. PCD elements of this type maybe used in almost any application where a hard wear and erosionresistant material is required. The substrate of the PCD element may bebrazed to a carrier, often also of cemented tungsten carbide. This is acommon configuration for PCD's used as cutting elements, for example infixed cutter or rolling cutter earth boring bits when received in asocket of the drill bit, or when fixed to a post in a machine tool formachining. These PCD elements are typically called polycrystallinediamond cutters (PDC).

[0007] There are numerous variations in the methods of manufacture ofthese PDC elements. For example various ranges of average diamondparticle sizes may be utilized in the manufacture to enhance wearproperties as shown in U.S. Pat. Nos. 4,861,350; 5,468,268; and5,545,748 all herein incorporated by reference for all they disclose.Also, methods to provide a range of wear resistance across or into theworking surface of a PDC are shown in U.S. Pat. Nos. 5,135,061 and5,607,024 also herein incorporated by reference for all they disclose.However, because the wear resistance is varied by changing the averagesize of the diamond particles, there is an inherent trade-off betweenimpact strength and wear resistance in these designs. As a consequence,the PDC elements with the higher wear resistance will tend to have poorimpact strength, which for PDC's used in drilling applications, is oftenunacceptable.

[0008] Typically, higher diamond volume densities in the diamond tableincreases wear resistance at the expense of impact strength. However,modern PDC elements typically utilize often complex geometricalinterfaces between the diamond table and the substrate as well as otherphysical design configurations to improve the impact strength. Althoughthis allows wear resistance and impact strength to be simultaneouslymaximized, the tradeoff still exists, and has not significantly changedfor the past several years prior to the present invention.

[0009] Another form of PCD element is a unitary PCD element without anintegral substrate where a table of polycrystalline diamond is fixed toa tool or wear surface by mechanical means or a bonding process. ThesePCD elements differ from those above in that diamond particles arepresent throughout the element. These PCD elements may be held in placemechanically, they may be embedded within a larger PCD element that hasa substrate, or, alternately, they may be fabricated with a metalliclayer which may be bonded with a brazing or welding process. A pluralityof these PCD elements may be made from a single PCD, as shown, forexample, in U.S. Pat. Nos. 4,481,016 and 4,525,179 herein incorporatedby reference for all they disclose.

[0010] PCD elements are most often formed by sintering diamond powderwith a suitable binder-catalyzing material in a high-pressure,high-temperature press. One particular method of forming thispolycrystalline diamond is disclosed in U.S. Pat. No. 3,141,746 hereinincorporated by reference for all it discloses. In one common processfor manufacturing PCD elements, diamond powder is applied to the surfaceof a preformed tungsten carbide substrate incorporating cobalt. Theassembly is then subjected to very high temperature and pressure in apress. During this process, cobalt migrates from the substrate into thediamond layer and acts as a binder-catalyzing material, causing thediamond particles to bond to one another with diamond-to-diamondbonding, and also causing the diamond layer to bond to the substrate.

[0011] The completed PCD element has at least one body with a matrix ofdiamond crystals bonded to each other with many interstices containing abinder-catalyzing material as described above. The diamond crystalscomprise a first continuous matrix of diamond, and the interstices forma second continuous matrix of interstices containing thebinder-catalyzing material. In addition, there are necessarily arelatively few areas where the diamond to diamond growth hasencapsulated some of the binder-catalyzing material. These “islands” arenot part of the continuous interstitial matrix of binder-catalyzingmaterial.

[0012] In one common form, the diamond body constitutes 85% to 95% byvolume and the binder-catalyzing material the other 5% to 15%. Such anelement may be subject to thermal degradation due to differentialthermal expansion between the interstitial cobalt binder-catalyzingmaterial and diamond matrix beginning at temperatures of about 400degrees C. Upon sufficient expansion the diamond-to-diamond bonding maybe ruptured and cracks and chips may occur.

[0013] Also in polycrystalline diamond, the presence of thebinder-catalyzing material in the interstitial regions adhering to thediamond crystals of the diamond matrix leads to another form of thermaldegradation. Due to the presence of the binder-catalyzing material, thediamond is caused to graphitize as temperature increases, typicallylimiting the operation temperature to about 750 degrees C.

[0014] Although cobalt is most commonly used as the binder-catalyzingmaterial, any group VIII element, including cobalt, nickel, iron, andalloys thereof, may be employed.

[0015] To reduce thermal degradation, so-called “thermally stable”polycrystalline diamond components have been produced as preform PCDelements for cutting and/or wear resistant elements, as disclosed inU.S. Pat. No. 4,224,380 herein incorporated by reference for all itdiscloses. In one type of thermally stable PCD element the cobalt orother binder-catalyzing material in conventional polycrystalline diamondis leached out from the continuous interstitial matrix after formation.Numerous methods for leaching the binder-catalyzing material are known.Some leaching methods are disclosed, for example, in U.S. Pat. Nos.4,572,722 and 4,797,241 both herein incorporated by reference for allthey disclose.

[0016] While leaching the binder-catalyzing material may increase thetemperature resistance of the diamond to about 1200 degrees C., theleaching process also removes the cemented carbide substrate. Inaddition, because there is no integral substrate or other bondablesurface, there are severe difficulties in mounting such material for usein operation.

[0017] The fabrication methods for this “thermally stable” PCD elementtypically produce relatively low diamond volume densities, typically ofthe order of 80 volume % or less. This low diamond volume densityenables a thorough leaching process, but the resulting finished part istypically relatively weak in impact strength. The low volume density istypically achieved by using an admixtures process and using relativelysmall diamond crystals with average particle sizes of about 15 micronsor less. These small particles are typically coated with a catalyzingmaterial prior to processing. The admixtures process causes the diamondparticles to be widely spaced in the finished product and relativelysmall percentages of their outer surface areas dedicated todiamond-to-diamond bonding, often less than 50%, contributing to the lowimpact strengths.

[0018] In these so-called “thermally stable” polycrystalline diamondcomponents, the lack of a suitable bondable substrate for laterattachment to a work tool has been addressed by several methods. Onesuch method to attach a bondable substrate to a “thermally stable”polycrystalline diamond preform is shown in U.S. Pat. No. 4,944,772herein incorporated by reference for all it discloses. In this process,a porous polycrystalline diamond preform is first manufactured, and thenit is re-sintered in the presence of a catalyzing material athigh-temperatures and pressures with a barrier layer of other materialwhich, in theory, prevents the catalyzing material from re-infiltratingthe porous polycrystalline diamond preform. The resulting producttypically has an abrupt transition between the preform and the barrierlayer, causing problematic stress concentrations in service. Thisproduct would be considered to be more a joined composite than anintegral body.

[0019] Other, similar processes to attach a bondable substrate to“thermally stable” polycrystalline diamond components are shown in U.S.Pat. Nos. 4,871,377 and 5,127,923 herein incorporated by reference forall they disclose. It is believed that the weakness of all theseprocesses is the degradation of the diamond-to-diamond bonds in thepolycrystalline diamond preform from the high temperature and pressurere-sintering process. It is felt that this destruction/disruptiongenerally further reduces the impact strength of the finished product toan unacceptably low level below that of the preform.

[0020] In an alternative form of thermally stable polycrystallinediamond, silicon is used as the catalyzing material. The process formaking polycrystalline diamond with a silicon catalyzing material isquite similar to that described above, except that at synthesistemperatures and pressures, most of the silicon is reacted to formsilicon carbide, which is not an effective catalyzing material. Thethermal resistance is somewhat improved, but thermal degradation stilloccurs due to some residual silicon remaining, generally uniformlydistributed in the interstices of the interstitial matrix. Again, thereare mounting problems with this type of PCD element because there is nobondable surface.

[0021] More recently, a further type of PCD has become available inwhich carbonates, such as powdery carbonates of Mg, Ca, Sr, and Ba areused as the binder-catalyzing material when sintering the diamondpowder. PCD of this type typically has greater wear-resistance andhardness than the previous types of PCD elements. However, the materialis difficult to produce on a commercial scale since much higherpressures are required for sintering than is the case with conventionaland thermally stable polycrystalline diamond. One result of this is thatthe bodies of polycrystalline diamond produced by this method aresmaller than conventional polycrystalline diamond elements. Again,thermal-degradation may still occur due to the residualbinder-catalyzing material remaining in the interstices. Again, becausethere is no integral substrate or other bondable surface, there aredifficulties in mounting this material to a working surface.

[0022] Other efforts to combine thermally stable PCD's with mountingsystems to put their improved temperature stability to use have not beenas successful as hoped due to their low impact strength. For example,various ways of mounting multiple PCD elements are shown in U.S. Pat.Nos. 4,726,718; 5,199,832; 5,025,684; 5,238,074; 6,009,963 hereinincorporated by reference for all they disclose. Although many of thesedesigns have had commercial success, the designs have not beenparticularly successful in combining high wear and/or abrasionresistance while maintaining the level of toughness attainable innon-thermally stable PCD.

[0023] Other types of diamond or diamond like coatings for surfaces aredisclosed in U.S. Pat. Nos. 4,976,324; 5,213,248; 5,337,844; 5,379,853;5,496,638; 5,523,121; 5,624,068 all herein incorporated by reference forall they disclose. Similar coatings are also disclosed in GB PatentPublication No. 2,268,768, PCT Publication No. 96/34,131, and EPCPublications 500,253; 787,820; 860,515 for highly loaded tool surfaces.In these publications, diamond and/or diamond like coatings are shownapplied on surfaces for wear and/or erosion resistance.

[0024] In many of the above applications physical vapor deposition (PVD)and/or chemical vapor deposition (CVD) processes are used to apply thediamond or diamond like coating. PVD and CVD diamond coating processesare well known and are described for example in U.S. Pat. Nos.5,439,492; 4,707,384; 4,645,977; 4,504,519; 4,486,286 all hereinincorporated by reference.

[0025] PVD and/or CVD processes to coat surfaces with diamond or diamondlike coatings may be used, for example, to provide a closely packed setof epitaxially oriented crystals of diamond or other superhard crystalson a surface. Although these materials have very high diamond densitiesbecause they are so closely packed, there is no significant amount ofdiamond to diamond bonding between adjacent crystals, making them quiteweak overall, and subject to fracture when high shear loads are applied.The result is that although these coatings have very high diamonddensities, they tend to be mechanically weak, causing very poor impacttoughness and abrasion resistance when used in highly loadedapplications such as with cutting elements, bearing devices, wearelements, and dies.

[0026] Some attempts have been made to improve the toughness and wearresistance of these diamond or diamond like coatings by application to atungsten carbide substrate and subsequently processing in ahigh-pressure, high-temperature environment as described in U.S. Pat.Nos. 5,264,283; 5,496,638; 5,624,068 herein incorporated by referencefor all they disclose. Although this type of processing may improve thewear resistance of the diamond layer, the abrupt transition between thehigh-density diamond layer and the substrate make the diamond layersusceptible to wholesale fracture at the interface at very low strains,similar to the above described problems encountered with compositestructures having barrier layers. This again translates to very poortoughness and impact resistance in service.

[0027] When PCD elements made with a cobalt or other group VIII metalbinder-catalyzing material were used against each other as bearingmaterials, it was found that the coefficient of friction tended toincrease with use. As described in U.S. Pat. No. 5,560,716 hereinincorporated by reference for all it discloses and corollary EuropeanPatent specification number 617,207, it was found that removal (by useof a hydrochloric acid wipe) of the cobalt-rich tribofilm which tendedto build up in service from the surface of the PCD bearing element,tended to temporarily mitigate this problem. It was speculated that,during operation, some of the cobalt from the PCD at the surfacemigrates to the load area of the bearing, causing increased frictionwhen two PCD elements act against each other as bearings. It is nowbelieved that the source of this cobalt may be-a residual by-product ofthe finishing process of the bearing elements, as the acid wipe remedycannot effectively remove the cobalt to any significant depth below thesurface.

[0028] Because the cobalt is removed only from the surface of the PCD,there is no effective change in the temperatures at which thermaldegradation occurs in these bearing elements. Therefore the deleteriouseffects of the binder-catalyzing material remain, and thermaldegradation of the diamond layer due to the presence of the catalyzingmaterial still occurs.

SUMMARY OF INVENTION

[0029] The present invention provides a superhard polycrystallinediamond or diamond-like element with greatly improved wear resistancewithout loss of impact strength. Collectively called PCD elements forthe purposes of this specification, these elements are formed with abinder-catalyzing material in a high-temperature, high-pressure (HTHP)process. The PCD element has a plurality of partially bonded diamond ordiamond-like crystals forming a continuous diamond matrix body with adiamond volume density greater than 85%. Interstices among the diamondcrystals form a continuous interstitial matrix containing a catalyzingmaterial. The diamond matrix table is formed and integrally bonded to asubstrate containing the catalyzing material during the HTHP process.The diamond matrix body has a working surface, where a portion of theinterstitial matrix in the body adjacent to the working surface issubstantially free of the catalyzing material, and the remaininginterstitial matrix contains the catalyzing material. Typically, lessthan about 70% of the body of the diamond matrix table is free of thecatalyzing material.

[0030] The working surface that is substantially free of the catalyzingmaterial is not subject to the thermal degradation encountered in theother areas of the working surface, resulting in improved wearresistance without loss of impact strength. In cutting elements, theprocessed working surface may be a portion of the facing table of thebody, a portion of the peripheral surface of the body, or portions ofall these surfaces.

[0031] In another embodiment, the catalyzing material is cobalt or otheriron group metal, and the method of depleting the catalyzing material isto leach it from the interstices near the surface of a PCD element in anacid etching process. It is anticipated that the method of removing thecatalyzing material from the surface may also be by electricaldischarge, or other electrical or galvanic process, or by evaporation.

[0032] A further method of manufacture of a PCD element comprising abody integrally formed with a metallic substrate, the body comprisingbonded diamond crystals and a catalyzing material is also disclosed. Thetreatment is performed by treating the body to render a volume thereofsubstantially free of the catalyzing material while permitting thecatalyzing material to remain in at least some of the remaining volumeof the body and while permitting the substrate to remain substantiallyunaffected when treating the body.

[0033] Disclosed is an element having a body comprising a plurality ofpartially bonded diamond crystals, a catalyzing material and aninterstitial matrix; the body having a working surface. The interstitialmatrix in the body adjacent to the working surface is substantially freeof the catalyzing material, and the remaining interstitial matrixcontains the catalyzing material.

[0034] Similarly, a PCD element is disclosed with a body having acatalyzing material, an interstitial matrix, and a working surface. Theinterstitial matrix in the body adjacent to the working surface issubstantially free of the catalyzing material, and the remaininginterstitial matrix contains the catalyzing material.

[0035] Furthermore, a PCD element is disclosed having a body with aworking surface. A first volume of the body remote from the workingsurface contains a catalyzing material, and a second volume of the bodyadjacent to the working surface is substantially free of the catalyzingmaterial.

[0036] A PCD element is also disclosed comprising a diamond containingbody integrally formed with a metallic substrate. The body has at leastan 85% by volume diamond density and an interstitial matrix. Theinterstitial matrix in the body adjacent to a working surface issubstantially free of the catalyzing material, and the interstitialregions where the body contacts the substrate contain the catalyzingmaterial and have an average thickness greater than 0.15 mm.

[0037] Furthermore, a PCD element is disclosed comprising a body ofbonded diamonds that has a working surface integrally formed with ametallic substrate. The body has at least an 85% by volume diamonddensity. A first volume of the body remote from the working surfacecontains a catalyzing material and a second volume of the body adjacentto the working surface is substantially free of the catalyzing material.

[0038] A PCD element is also disclosed comprising a body integrallyformed with a metallic substrate. The body has a plurality of bondeddiamond crystals having surfaces and a catalyzing material. The bodyalso has at least an 85% by volume diamond density. At least 30% of thecrystals in the body contact the catalyzing material and the surfaces ofa majority of the remaining crystals that are within at least a 0.1 mmdepth from a working surface are substantially free of the catalyzingmaterial.

[0039] In addition, a preform cutting element is disclosed. The cuttingelement comprises a body of a superhard polycrystalline materialcomprising a plurality of partially bonded superhard crystals integrallyformed with a metallic substrate, a plurality of interstitial regionsamong the superhard crystals and a catalyzing material. The body has atleast an 85% by volume diamond density and a cutting surface. Theinterstitial regions adjacent to at least a portion of the cuttingsurface are substantially free of the catalyzing material and at least30% of the remaining interstitial regions contain the catalyzingmaterial.

[0040] The PCD elements of the present invention may be used for wear,cutting, drawing, and other applications where engineered diamondsurfaces are needed. Specific applications are as cutting elements inrotary drill bits of both the fixed cutter type and the rolling cuttertype, as hollow dies, heat sinks, friction bearings, valve surfaces,indentors, tool mandrels, etc. The PCD element of the present inventionmay be used to machine abrasive wood products, ferrous and nonferrousmaterials and also very hard or abrasive engineering materials such asstone and asphalt and the like.

BRIEF DESCRIPTION OF DRAWINGS

[0041]FIG. 1A is a typical PCD element of the present invention.

[0042]FIG. 1B is a typical PCD of the present invention shown as acutting element.

[0043]FIG. 2 is a side view of a fixed cutter rotary drill bit using aPCD element of the present invention.

[0044]FIG. 3 is a perspective view of a rolling cutter rotary drill bitusing a PCD element of the present invention.

[0045]FIG. 4 is a perspective view of an insert used in machine toolsutilizing the PCD element of the present invention.

[0046]FIG. 5 is a perspective view of a dome shaped PCD element suitablefor use in both rolling cutter drill bits and in fixed cutter drillbits.

[0047]FIG. 6 is a photo-micrograph of the surface of a PCD element ofthe prior art showing the binder-catalyzing material in the interstitialregions.

[0048]FIG. 7 is a photo-micrograph of the PCD element of the presentinvention showing a first portion with a catalyzing material in theinterstitial regions and a second portion without the catalyzingmaterial in the interstitial regions.

[0049]FIG. 8 is a micro-structural representation of a PCD element ofthe prior art, showing the bonded diamond crystals, with theinterstitial regions and the random crystallographic orientation of theindividual crystals.

[0050]FIG. 9 is a micro-structural representation of the PCD element ofthe present invention as shown in FIG. 7, indicating the depth of thecatalyzing material free region relative to the surface of the PCDelement.

[0051]FIG. 10 is a graph of the relative wear indices of severalembodiments of the PCD element of the present invention.

[0052]FIG. 11A is a front view of an encapsulated PCD embodiment of thePCD element of the present invention.

[0053]FIG. 11B is a section view of another encapsulated PCD embodimentof the PCD element of the present invention.

[0054]FIG. 11C is a section view of still another encapsulated PCDembodiment of the PCD element of the present invention.

[0055]FIG. 12A is perspective view of a CVD/PVD applied surface foranother embodiment of the PCD element of the present invention.

[0056]FIG. 12B is an enlarged perspective view of the crystal structureof the embodiment of the PCD element of the present invention shown inFIG. 12A.

[0057]FIG. 13 is a section view of a wire drawing die having a PCDelement of the present invention.

[0058]FIG. 14 is perspective view of a heat sink having a PCD element ofthe present invention.

[0059]FIG. 15 is perspective view of a bearing having a PCD element ofthe present invention.

[0060]FIGS. 16A and 16B are front views of the mating parts of a valvehaving a PCD element of the present invention.

[0061]FIG. 17A is a side view of an indentor having a PCD element of thepresent invention.

[0062]FIG. 17B is a partial section view of a punch having a PCD elementof the present invention.

[0063]FIG. 18 is perspective view of a measuring device having a PCDelement of the present invention.

[0064]FIG. 19 is a graph representing the typical abrasive wearresistance vs. impact resistance of the prior art cutting elementscompared with a cutting element of the present invention.

DETAILED DESCRIPTION

[0065] The polycrystalline diamond or diamond-like material (PCD)element 2 of the present invention is shown in FIG. 1A. The PCD element2 has a plurality of partially bonded superhard, diamond ordiamond-like, crystals 60, (shown in FIGS. 7 and 9) a catalyzingmaterial 64, and an interstitial matrix 68 formed by the interstices 62among the crystals 60. The element 2 also has one or more workingsurfaces 4 and the diamond crystals 60 and the interstices 62 form thevolume of the body 8 of the PCD element 2. Preferably, the element 2 isintegrally formed with a metallic substrate 6, typically tungstencarbide with a cobalt binder material. To be effective when used in anabrasive wear application, the volume density of the diamond in the body8 must be greater than 85 volume %, and preferably be higher than 90%.

[0066] The working surface 4 is any portion of the PCD body 8 which, inoperation, may contact the object to be worked. In this specification,when the working surface 4 is discussed, it is understood that itapplies to any portion of the body 8 which may be exposed and/or used asa working surface. Furthermore, any portion of any of the workingsurface 4 is, in and of itself, a working surface.

[0067] During manufacture, under conditions of high-temperature andhigh-pressure (HTHP), the interstices 62 among the crystals 60 fill withthe catalyzing material 64 followed by bonds forming among the crystals60. In a further step of the manufacture, some of the catalyzingmaterial 64 is selectively depleted from some of the interstices 62. Theresult is that a first volume of the body 8 of the PCD element 2 remotefrom the working surface 4 contains the catalyzing material 64, and asecond volume of the body 8 adjacent to the working surface 4 issubstantially free of the catalyzing material 64. The interstices 62which are substantially free of the catalyzing material 64 are indicatedby numeral 66.

[0068] Therefore, the interstitial matrix 68 of the body 8 adjacent toat least a portion of the working surface 4 is substantially free of thecatalyzing material 64, and the remaining interstitial matrix 68contains the catalyzing material 64. As previously stated, the PCDelement 2 is preferably bonded in the HPHT process to a substrate 6 ofless hard material, usually cemented tungsten carbide or other metallicmaterial, but use of a substrate 6 is not required.

[0069] Because the body adjacent to the working surface 4 issubstantially free of the catalyzing material 64, the deleteriouseffects of the binder-catalyzing material 64 are substantiallydecreased, and thermal degradation of the working surface 4 due to thepresence of the catalyzing material 64 is effectively eliminated. Theresult is a new PCD element 2 that has the enhanced thermal propertiesapproximating that of the so called thermally stable PCD elements, whilemaintaining the toughness, convenience of manufacture, and bondingability of the traditional PDC elements. This translates to higher wearresistance in cutting applications, higher heat transfer capacity inheat sink applications, higher load capacity in bearing applications,less surface distortion in valve applications, and has advantages innumerous other applications including hollow dies, indentors, toolmandrels, and wear elements. These benefits are gained without loss ofimpact strength in the elements. Details of specific applications of thenew PCD element 2 will be discussed in more detail later in thespecification.

[0070] Referring now to the photo-micrograph of a prior art PCD elementin FIG. 6, and also the microstructural representation of a PCD elementof the prior art in FIG. 8, it is well known that there is a randomcrystallographic orientation of the diamond or diamond-like crystals 60as shown by the parallel lines representing the cleavage planes of eachcrystal 60. As can be seen, adjacent crystals 60 have bonded togetherwith interstitial spaces 62 among them. Because the cleavage planes areoriented in different directions on adjacent crystals 60 there isgenerally no straight path available for diamond fracture. Thisstructure allows PCD materials to perform well in extreme loadingenvironments where high impact loads are common.

[0071] In the process of bonding the crystals 60 in a high-temperature,high-pressure press, the interstitial spaces 62 among the crystals 60become filled with a binder-catalyzing material 64. It is thiscatalyzing material 64 that allows the bonds to be formed betweenadjacent diamond crystals 60 at the relatively low pressures andtemperatures present in the press.

[0072] The prior art PCD element has at least one continuous matrix ofcrystals 60 bonded to each other with the many interstices 62 containinga binder-catalyzing material 64, typically cobalt or other group VIIIelement. The crystals 60 comprise a first continuous matrix of diamond,and the interstices 62 form a second continuous matrix known as theinterstitial matrix 68, containing the binder-catalyzing material. Inaddition, there are necessarily a relatively few areas where the diamondto diamond growth has encapsulated some of the binder-catalyzingmaterial. These “islands” are not part of the continuous interstitialmatrix 68 of binder-catalyzing material 64.

[0073] Referring now to FIGS. 7 and 9, shown is a cross section of thePCD element 2 of the present invention. The PCD element 2 may be formedin the same manner as the prior art PCD elements described above. In apreferred embodiment, after a preliminary cleanup operation or at anytime thereafter in the process of manufacturing, the working surface 4,70, 72 of the PCD element 2 is processed in a manner which removes aportion of the binder-catalyzing material from the adjacent body. Theresult is that the interstices 62 among the diamond crystals 60 adjacentto the working surface are substantially free of the catalyzing material64 indicated by numeral 66. The portion of the working surface 4, 70, 72that is free of the catalyzing material 64 is not subject to the thermaldegradation encountered in the other areas of the PCD, resulting inimproved thermal characteristics.

[0074] The average diamond volume density in the body 8 of the PCDelement 2 of the present invention ranges from about 85% to about 99%.The high diamond volume density is achieved by using diamond crystals 60with a range of particle sizes, with an average particle size rangingfrom about 30 to about 60 microns. Typically, the diamond mixture maycomprise 20% to 60% diamond crystals 60 in the 5-15 micron range, 20% to40% diamond crystals 60 in the 25-40 micron range, and 20% to 40%diamond crystals 60 in the 50-80 micron diameter range, althoughnumerous other size ranges and percentages may be used. This mixture oflarge and small diamond crystals 60 allows the diamond crystals 60 tohave relatively high percentages of their outer surface areas dedicatedto diamond-to-diamond bonding, often approaching 95%, contributing to arelatively high apparent abrasion resistance.

[0075] There are many methods for removing or depleting the catalyzingmaterial 64 from the interstices 62. In one method, the catalyzingmaterial 64 is cobalt or other iron group material, and the method ofremoving the catalyzing material 64 is to leach it from the interstices62 near the working surface 4, 70, 72 of a PCD element 2 in an acidetching process to a depth of greater than about 0.2 mm. It is alsopossible that the method of removing the catalyzing material 64 fromnear the surface may be by electrical discharge, or other electrical orgalvanic process or by evaporation.

[0076] In another method for depleting the catalyzing material 64 fromthe interstices 62, the catalyzing material 64 is depleted by combiningit chemically, such as alloying, with another material such that it nolonger acts as a catalyzing material. In this method, a material mayremain in the interstices among the diamond crystals 60, but thatmaterial no longer acts as a catalyzing material 64 effectively removingit.

[0077] In still another method for depleting the catalyzing material 64from the interstices 62, the catalyzing material 64 is removed bycausing it to transform into a material that no longer acts as acatalyzing material. This may be accomplished by a crystal structurechange, phase change, mechanical “working”, thermal treatment or othertreatment methods. This method may apply to non-metallic or non-reactivecatalyzing materials. Again, a material may remain in the interstices 62among the diamond crystals, but that material no longer acts as acatalyzing material 64 effectively removing the catalyzing material.

[0078] Once the catalyzing material 64 adjacent to the working surface4, 70, 72 has been rendered ineffective, the PCD element 2 of thepresent invention is no longer susceptible to the type of thermaldegradation known to occur in the prior art PCD elements. As previouslydescribed, there are two modes of thermal degradation known to be causedby the catalyzing material 64. The first mode of thermal degradationbegins at temperatures as low as about 400 degrees C and is due todifferential thermal expansion between the catalyzing material 64 in theinterstices 62 and the crystals 60. Upon sufficient expansion thediamond-to-diamond bonding may be ruptured and cracks and chips mayoccur.

[0079] The second mode of thermal degradation begins at temperatures ofabout 750 degrees C. This mode is caused by the catalyzing ability ofthe binder-catalyzing material 64 contacting the crystals 60, andcausing the crystals 60 to graphitize as the temperature exceeds about750 degrees C. As the crystals 60 graphitize, they undergo a huge volumeincrease resulting in cracking and dis-bond from the body 4. Even acoating of a few microns of the catalyzing material 64 on the surfacesof the diamond crystals 60 can enable this mode of thermal degradation.

[0080] It would therefore be appreciated by those skilled in the artthat for maximum benefit, the catalyzing material 64 must be removedboth from the interstices 62 among the diamond crystals 60 and from thesurfaces of the diamond crystals 60 as well. If the catalyzing material64 is removed from both the surfaces of the diamond crystals 60 and fromthe interstices 62 the onset of thermal degradation for the diamondcrystals 60 in that region would approach 1200 C.

[0081] This dual degradation mode, however, provides some unexpectedbenefits. For example, in many applications it is desirable to engineerthe wear rate of the working surface. In the present invention, this maybe accomplished by changing the treatment process such that in areasrequiring maximum wear resistance, the catalyzing material is depletedfrom both the interstices 62 and the surfaces of the diamond crystals60. In areas where less wear resistance is desired, for example in aself sharpening tool, those areas would be treated so as to deplete thecatalyzing material 64 primarily from the interstices 62, but allowingsome, if not all, of the diamond crystals 60 to remain in contact withthe catalyzing material.

[0082] It should also be apparent, that it is more difficult to removethe catalyzing material 64 from the surfaces of the diamond crystals 60than from the interstices 62. For this reason, depending upon the mannerin which the catalyzing material is depleted, to be effective inreducing thermal degradation, the depth of depletion of the catalyzingmaterial 64 from the working surface 4 may vary depending upon themethod used for depleting the catalyzing material 64.

[0083] In some applications, improvement of the thermal threshold toabove 400 C. but less than 750 C. is adequate, and therefore a lessintense catalyzing material 64 depletion process is permissible. As aconsequence, it would be appreciated that there are numerouscombinations of catalyzing material 64 depletion methods which could beapplied to achieve the level of catalyzing material 64 depletionrequired for a specific application.

[0084] In this specification, when the term “substantially free” is usedreferring to catalyzing material 64 in the interstices 62, theinterstitial matrix 68, or in a volume of the body 8, it should beunderstood that many, if not all, the surfaces of the adjacent diamondcrystals 60 may still have a coating of the catalyzing material 64.Likewise, when the term “substantially free” is used referring tocatalyzing material 64 on the surfaces of the diamond crystals 60, theremay still be catalyzing material 64 present in the adjacent interstices62.

[0085] With the catalyzing material 64 removed or depleted, two majormechanisms for thermal degradation are no longer present. However, ithas been found that the catalyzing material 64 has to be removed at adepth sufficient to allow the bonded crystals 60 to conduct away theheat generated by a thermal event to below the degradation temperatureof the crystals 60 where the catalyzing material 64 is present.

[0086] In one set of laboratory tests, heat was input into a PCD element2 configured as a cutting element 10. Since this test was designed as astandard wear test for these cutting elements, it provided a reasonablecomparison of cutting elements 10 with various depths of the catalyzingmaterial 64 removal. In these tests, care was taken to assure thedepletion process removed the catalyzing material 64 from both theinterstices 62 and from the surfaces of the diamond crystals 60. Thetest was designed such that a repeatable input of heat was applied tothe cutting edge of the PCD cutting element 10 for a known period oftime.

[0087] Once the test was complete, a wear index was calculated. Thehigher the wear index, the better the wear resistance. Due to the natureof the test, it is assumed that an increased wear index number indicatesincreased resistance to thermal degradation of the working surface 70,72 of the cutting element 10.

[0088] As can be seen in curve A in the graph of FIG. 10 there is adramatic increase in the wear index result for cutting elements 10 whenthe catalyzing material 64 depletion depth approaches 0.1 mm. Therefore,for the types of heat input common in cutting elements 10, a 0.1 mmdepth is the critical depletion depth from the working surface 4, 70, 72when the catalyzing material 64 is removed from both interstices 62 andfrom the surfaces of the diamond crystals 60.

[0089] In other tests, on cutting elements 10 made with a moreeconomical process for removing the catalyzing material 64, the wearversus depth of depletion is believed to approximate that shown in curve“B” of FIG. 10. The catalyzing material 64 depletion process used inthese cutters was not as effective for removing the catalyzing material64 from the surfaces of the diamond crystals 60 as the process of curve“A”. Therefore, it was not until most of the catalyzing material 64 wasremoved from the interstices 62 to a depth of about 0.2 mm that the wearrate improved to that of curve “A”. It was found that the impactstrength of these cutting elements 10 was substantially unchanged fromuntreated elements.

[0090] Referring now to FIG. 19, to visually demonstrate the comparisonof the invention's improvement in wear resistance while maintainingimpact strength, a typical, impact resistance VS abrasive wearresistance curve well known and well established for prior art cuttingelements is indicated by curve W. The point P on the graph relativelyindicates the properties of the cutting element of the presentinvention. As can be seen, P lies in the top right corner area of thegraph, which represents to those skilled in the art, a significant andsubstantial improvement in wear resistance of cutting elements whilemaintaining impact strength.

[0091] It is believed that thermal degradation relating to wear rates asshown in curve “C” of FIG. 10 can be engineered into PCD elements 2where it is beneficial. For example, it may be desirable to have edgesof curved cutting elements 10 remote from the center of contact to wearmore quickly than the center point. This would tend to preserve thecurved shape of the cutting element, rather than having it become a flatsurface.

[0092] Improved thermal degradation resistance improves wear ratesbecause diamond is an extremely good thermal conductor. If a frictionevent at working surface 4, 70, 72 caused a sudden, extreme heat input,the bonded diamond crystals would conduct the heat in all directionsaway from the event. This would permit an extremely high temperaturegradient through the material, possibly 1000 C. per mm or higher. Agradient this steep would enable the working surface 4, 70, 72 to reach950 C., and not cause significant thermal degradation if interstices 62and the surfaces of the diamond crystals 62 adjacent to the workingsurface are substantially free of the catalyzing material 64 to a depthof just 0.2 mm from the source of the heat.

[0093] It should be apparent that the temperature gradient will varydepending upon the crystal 60 size and the amount of inter-crystalbonding. One convenient way to characterize this is the volume densityof the diamond in the body 8. Under normal manufacturing methods, as thevolume density of the diamond increases, the potential temperaturegradient through the material also increases. This implies that amaterial otherwise identical that which produced curve “B” in FIG. 10,save for an increased diamond volume density, would subsequently producea wear index closer to the curve “A” in FIG. 10.

[0094] In field tests of cutting elements 10 for earth boring bits,removal of substantially all of the catalyzing material 64 from theinterstices 62 to a distance D of about 0.2 mm to about 0.3 mm from aworking surface 4, 70, 72 produced dramatic improvements in wearresistance, with a combination of a 40% increase in rate of penetrationand a 40% improvement in wear resistance without loss of impactstrength. The improvement in wear resistance indicates that theattrition of the diamond crystals 60 due to catalyzing material 64induced thermal degradation was dramatically reduced. The rate ofpenetration increase is believed to be due to the ability of the cutterto remain “sharper” longer due to the increased wear resistance.

[0095] It is believed, however, that as the volume density of thediamond in the body 8 increases from the 85%-90% range to the 95%-99%range, the distance D needed to produce a particular wear index willdecrease. Therefore, it is also believed that a distance D of less than0.1 mm could provide approximately the same wear index in a cuttingelement with a diamond density of the body approaching 99% as the 0.2 mmto 0.3 mm D distance in a body with 85% to 90% diamond volume density.

[0096] It is important when removing the catalyzing material 64 from theinterstices 62 that the underlying substrate 6, 32 is not also affected.It is therefore very important that at least a portion of the diamondlayer has the catalyzing material 64 remaining in the interstices 62. Ithas been found that when depleting the catalyzing material 64 from aflat surface having a planar interface with the substrate 6, 32, a layerwith a minimum thickness of about 0.15 mm containing the catalyzingmaterial 64 must remain to assure that the underlying substrate 6, 32 isnot affected.

[0097] Quantifying this amount for PDC's in general is problematic,because some interaction of the depletion process and the substrate canbe tolerated, and geometries can be complex. However, one way toquantify this is that the portion of the body 8 contacting the substrate6,32 must have the catalyzing material 64 remaining in the interstices62 to an average thickness of greater than 0.15 mm.

[0098] Another way to quantify this is to express the minimum amount ofcatalyzing material 64 remaining in the interstices 62 as a volumepercent. It is known that with a very thin, flat diamond layer, a 0.15mm layer containing the catalyzing material 64 is required in a 0.5 mmthick body. It is therefore reasonable to assume that a minimum of 30%of the volume of the body 8 must have interstices 62 containing thecatalyzing material 64 for PDC elements of the present invention,particularly with the size ranges of typically used PDC cutters.

[0099] There are other possible constructions of PCD elements thatbenefit from depletion or removal of the catalyzing material 64 asdescribed above. As shown in FIGS. 1A, 1B and 1C another embodiment ofthe present invention is a compound PCD element 102. The PCD element 102has a body 108 with a group VIII binder-catalyzing material with asecond preformed PCD element 110 embedded within it. The embedded PCDelement 110 may be flush with the working surface 104 of theencapsulating PCD element 120 as shown in FIG. 11A, or it may beembedded wholly within the encapsulating PCD element 120 as shown inFIG. 11B. This embedded PCD element 110 is made in a process usingpowdery carbonates of Mg, Ca, Sr, and Ba as the binder-catalyzingmaterial, and is formed into a compound PCD element as described in thecommonly assigned co-pending U.S. patent application Ser. No.09/390,074, now U.S. Pat. No. 6,248,447 herein incorporated byreference.

[0100] In this embodiment, since the embedded preformed PCD element 110is formed at higher pressures, the diamond density may be made higherthan that of the encapsulating PCD element 120. In this constructionsince the embedded PCD element 110 has a catalyzing material with ahigher activation temperature, it may for example, be beneficial todeplete the catalyzing material only in the working surface of theencapsulating PCD element 120. Furthermore, the embedded PCD element 110may be positioned within the encapsulating PCD element 120 to takeadvantage of the higher impact resistance of the embedded PCD element110 combined with the improved wear resistance of the encapsulatingelement 120.

[0101] As shown in FIGS. 9, 11A, 11B, and 11C, the element 102 has aplurality of partially bonded diamond crystals 60, a catalyzing material64 and a body 108 with a working surface 104. The volume 112 of the bodyadjacent the working surface 104 has a substantially higher diamonddensity than elsewhere 114 in the body 108, and the volume 112 issubstantially free of the catalyzing material 64.

[0102] Several embedded PCD elements 110 may be arranged in the compoundelement 100, as shown in FIG. 11C, in a manner where the best of bothimpact resistance and improved wear resistance may be realized.

[0103] It may be desirable to deplete the catalyzing material in theembedded PCD element 110 as well as the catalyzing material of theencapsulating PDC element 120. This combination would provide an elementwith the highest possible impact strength combined with the highestpossible wear resistance available in diamond elements for commercialuse.

[0104] In FIGS. 12A and 12B another embodiment of the PCD element 202 ofthe present invention is shown. In this embodiment, the PCD element 202is first formed in the manner of the prior art. After a surface has beenprepared, a CVD or PVD process is used to provide a closely packed setof epitaxially oriented crystals of diamond 260 deposited upon a futureworking surface 204 on a portion 210 of the PCD element 202. Theassembly is then subjected to a high-pressure high-temperature processwhereby the deposited diamond crystals 260 form diamond to diamond bondswith each other, and to the diamond crystals in the parent PCD. Thisdiamond-to-diamond bonding is possible due to the presence of thecatalyzing material 64 infusing from the surface of parent PCD element202.

[0105] After cleanup, a portion of the working surface 204 is treated todeplete the catalyzing material 64 from the CVD or PVD deposited layer.The final product is a PCD element having one portion of a workingsurface 204 with a volume 214 much higher in diamond density than thatof the other surfaces 280 of the PCD element 202. This region 214 ofhigh diamond density is subsequently depleted of the catalyzing material64. Portions of the other surfaces 280 of the PCD element 202 may bedepleted of the binder catalyzing material as well.

[0106] In general the elements 102, 202 shown in FIGS. 11A, 11B, 11C,12A, and 12B may be characterized as PCD element 102, 102 having a body108, 208 with a working surface 104, 204. The diamond density adjacentthe working surface 104, 204 is substantially higher than elsewhere inthe body 108, 208, and is substantially free of the catalyzing material64.

[0107] One particularly useful application for the PCD element 2 of thepresent invention is as cutting elements 10, 50, 52 as shown in FIGS.1B, 4 and 5. The working surface of the PCD cutting elements 10, 50, 52may be a top working surface 70 and/or a peripheral working surface 72.The PCD cutting element 10 of FIG. 1B is one that may be typically usedin fixed cutter type rotary drill bits 12, or for gauge protection inother types of downhole tools. The PCD cutting element 50 shown in FIG.5 may be shaped as a dome 39. This type of PCD cutting element 50 has anextended base 51 for insertion into sockets in a rolling cutter drillbit 38 or in the body of both types of rotary drill bits, 12, 38 as willbe described in detail.

[0108] The PCD cutting element 52 of FIG. 4 is adapted for use in amachining process. Although the configuration of the cutting element 52in FIG. 4 is rectangular, it would be appreciated by those skilled inthe art that this element could be triangular, quadrilateral or manyother shapes suitable for machining highly abrasive products that aredifficult to machine with conventional tools.

[0109] The PCD cutting element 1 0 may be a preform cutting element 10of a fixed cutter rotary drill bit 12 (as shown in FIG. 2). The bit body14 of the drill bit is formed with a plurality of blades 16 extendinggenerally outwardly away from the central longitudinal axis of rotation18 of the drill bit. Spaced apart side-by-side along the leading face 20of each blade is a plurality of the PCD cutting elements 10 of thepresent invention.

[0110] Typically, the PCD cutting element 10 has a body in the form of acircular tablet having a thin front facing table 30 of diamond ordiamond-like (PCD) material, bonded in a high-pressure high-temperaturepress to a substrate 32 of less hard material such as cemented tungstencarbide or other metallic material. The cutting element 10 is preformedand then typically bonded on a generally cylindrical carrier 34 which isalso formed from cemented tungsten carbide, or may alternatively beattached directly to the blade. The PCD cutting element 10 has workingsurfaces 70 and 72.

[0111] The cylindrical carrier 34 is received within a correspondinglyshaped socket or recess in the blade 16. The carrier 34 will usually bebrazed or shrink fit in the socket. In operation the fixed cutter drillbit 12 is rotated and weight is applied. This forces the cuttingelements 10 into the earth being drilled, effecting a cutting and/ordrilling action.

[0112] The PCD cutting elements 10 may also be applied to the gaugeregion 36 of the bit 12 to provide a gauge reaming action as well asprotecting the bit 12 from excessive wear in the gauge region 36. Inorder to space these cutting elements 10 as closely as possible, it maybe desirable to cut the elements into shapes, such as the rectangularshape shown, which more readily fit into the gauge region 36.

[0113] In a second embodiment, the cutting element 50 (as shown in FIG.5) of the present invention is on a rolling cutter type drill bit 38,shown in FIG. 3. A rolling cutter drill bit 38 typically has one or moretruncated rolling cone cutters 40, 41, 42 assembled on a bearing spindleon the leg 44 of the bit body 46. The cutting elements 50 may be mountedas one or more of a plurality of cutting inserts arranged in rows onrolling cutters 40, 41, 42, or alternatively the PCD cutting elements 50may be arranged along the leg 44 of the bit 38. The PCD cutting element50 has a body in the form of a facing table 35 of diamond or diamondlike material bonded to a less hard substrate 37. The facing table 35 inthis embodiment of the present invention is in the form of a domedsurface 39 and has working surfaces 70 and 72. Accordingly, there areoften a number of transitional layers between the facing table 35 andthe substrate 37 to help more evenly distribute the stresses generatedduring fabrication, as is well known to those skilled in the art.

[0114] In operation the rolling cutter drill bit 38 is rotated andweight is applied. This forces the cutting inserts 50 in the rows of therolling cone cutters 40, 41, 42 into the earth, and as the bit 36 isrotated the rolling cutters 40, 41, 42 turn, effecting a drillingaction.

[0115] In another embodiment, the PCD cutting element 52 of the presentinvention is in the form of a triangular, rectangular or other shapedmaterial for use as a cutting insert in machining operations. In thisembodiment, the cutting element 52 has a body in the form of a facingtable 54 of diamond or diamond like material bonded to a less hardsubstrate 56 with working surfaces 70 and 72. Typically, the cuttingelement 52 would then be cut into a plurality of smaller pieces whichare subsequently attached to an insert 58 that is mounted in the toolholder of a machine tool. The cutting element 52 may be attached to theinsert by brazing, adhesives, welding, or clamping. It is also possibleto finish form the cutting element 52 in the shape of the insert in ahigh-temperature high-pressure manufacturing process.

[0116] As shown in FIGS. 13-18, PCD elements 2, 102, 202 of the presentinvention may also be used for other applications such as hollow dies,shown for example as a wire drawing die, 300 of FIG. 13 utilizing a PCDelement 302 of the present invention. It may also be desirable toutilize the excellent heat transfer capabilities of the PCD element 2,102, 202 along with its electrical insulation properties as a heat sink310 with a PCD element 312 of the present invention.

[0117] Other applications include friction bearings 320 with a PCDbearing element 322 shown in FIG. 15 and the mating parts of a valve340, 344 with surfaces 342 having a PCD element 342 of the presentinvention as shown in FIGS. 16A and 16B. In addition, indentors 360 forscribes, hardness testers, surface roughening, etc. may have PCDelements 362 of the present invention as shown in FIG. 17A. Punches 370may have either or both dies 372, 374 made of the PCD material of thepresent invention, as shown in FIG. 17B. Also, tool mandrels 382 andother types of wear elements for measuring devices 380, shown in FIG. 18may be made of PCD elements of the present inventions. It should beunderstood that almost every application for polycrystalline diamondwould benefit from the catalyzing material depleted PCD elements of thepresent invention.

[0118] Whereas the present invention has been described in particularrelation to the drawings attached hereto, it should be understood thatother and further modifications apart from those shown or suggestedherein, may be made within the scope and spirit of the presentinvention.

What is claimed is:
 1. A method of manufacture of a PCD elementcomprising a body and a metallic substrate, the body comprising bondeddiamond crystals and a catalyzing material, and a working surface on thebody, by treating the body to render a volume adjacent to the workingsurface thereof substantially free of the catalyzing material to a depthof at least about 0.1 mm from the working surface while permitting thecatalyzing material to remain in at least some of the remaining volumeof the body and while permitting the substrate to remain substantiallyunaffected when treating the body.
 2. The method of claim 1, wherein thevolume is rendered substantially free of catalyzing material by leachingthe catalyzing material from the volume.
 3. The method of claim 1,wherein the volume is rendered substantially free of catalyzing materialby converting the catalyzing material to a form in which it does nothave a catalyzing effect.
 4. The method of claim 1, wherein the volumeis rendered substantially free of catalyzing material by reacting thecatalyzing material to form a substance which does not have a catalyzingeffect.
 5. The method of claim 1, wherein the volume is renderedsubstantially free of catalyzing material by electrical discharge. 6.The method of claim 1, wherein the volume is rendered substantially freeof catalyzing material using a galvanic process.
 7. The method of claim1, wherein the volume is rendered substantially free of catalyzingmaterial using an evaporation process.